U.S. patent application number 13/414069 was filed with the patent office on 2012-09-06 for implantable mems intraocular pressure sensor devices and methods for glaucoma monitoring.
This patent application is currently assigned to OrthoMEMS, Inc.. Invention is credited to Douglas A. Lee, Vernon G. Wong.
Application Number | 20120226133 13/414069 |
Document ID | / |
Family ID | 43759044 |
Filed Date | 2012-09-06 |
United States Patent
Application |
20120226133 |
Kind Code |
A1 |
Wong; Vernon G. ; et
al. |
September 6, 2012 |
IMPLANTABLE MEMS INTRAOCULAR PRESSURE SENSOR DEVICES AND METHODS
FOR GLAUCOMA MONITORING
Abstract
An implantable device for measuring IOP comprises a distal
portion, a proximal portion and a conformable elongate support
extending between the distal portion and the proximal portion. The
distal portion comprises a pressure sensor, for example a
capacitor, and the proximal portion comprises a coil. The
conformable elongate support extends between the distal portion and
the coil so as to couple the distal portion to the coil, and the
conformable elongate support is sized to position the sensor in the
anterior chamber when the proximal portion is positioned under a
conjunctiva of the eye. Positioning of the pressure sensor in the
anterior chamber has the benefit of readily accessible surgical
access and a direct measurement of the IOP of the eye. The proximal
portion comprising the coil can be configured to place the coil
between the sclera and the conjunctiva, such that the invasiveness
of the surgery can be decreased substantially.
Inventors: |
Wong; Vernon G.; (Menlo
Park, CA) ; Lee; Douglas A.; (Menlo Park,
CA) |
Assignee: |
OrthoMEMS, Inc.
Menlo Park
CA
|
Family ID: |
43759044 |
Appl. No.: |
13/414069 |
Filed: |
March 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2010/049461 |
Sep 20, 2010 |
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13414069 |
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61243847 |
Sep 18, 2009 |
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61335562 |
Jan 8, 2010 |
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Current U.S.
Class: |
600/398 |
Current CPC
Class: |
A61B 2562/028 20130101;
A61B 5/6846 20130101; A61B 3/16 20130101 |
Class at
Publication: |
600/398 |
International
Class: |
A61B 3/16 20060101
A61B003/16 |
Claims
1. A method of implanting a pressure sensor for measuring an
intraocular pressure of an eye having an anterior segment and a
conjunctiva, the method comprising: providing the implant having a
distal portion comprising the pressure sensor, a proximal portion,
and a conformable elongate support extending between the proximal
portion and the distal portion; and inserting the distal portion
comprising the pressure sensor into the anterior segment to measure
the intraocular pressure such that at least a portion of the
conformable elongate support extends from under the conjunctiva to
the anterior chamber.
2. The method of claim 1, wherein the anterior segment comprises an
anterior chamber and a posterior chamber and wherein a transducer
of the sensor is positioned within the anterior chamber.
3. The method of claim 1, wherein the elongate support conforms to
tissue disposed between the conjunctiva and the distal end.
4. The method of claim 1, wherein the elongate support is bent
prior to placement in the eye to position the sensor in the
anterior chamber.
5. The method of claim 4, wherein the elongate support is bent to
correspond with a curve.
6. The method of claim 5, wherein the curve comprises a prescribed
curve determined prior to insertion of the distal portion into the
anterior chamber of the eye.
7. The method of claim 1, wherein a channel is formed in a limbus
of the eye disposed between the conjunctiva and the aqueous humor,
the channel extending to the aqueous humor, and wherein the distal
portion and the elongate support are inserted into the channel.
8. The method of claim 1, wherein the pressure sensor comprises a
pressure transducer positioned in the anterior chamber and
responsive to pressure of the anterior chamber.
9. The method of claim 8, wherein a complaint material is disposed
over the transducer and positioned in the anterior chamber such
that the compliant material transmits pressure to the
transducer.
10. The method of claim 9, wherein the pressure sensor comprises
the transducer and the compliant material and wherein the complaint
material is positioned along a 360 degree perimeter around the
transducer such that the pressure sensor is responsive to pressure
along the 360 degree perimeter.
11. The method of claim 8, wherein the transducer comprises a
capacitor positioned in the anterior chamber and responsive to
pressure of the anterior chamber.
12. The method of claim 11, wherein a complaint material is
disposed over the capacitor and positioned in the anterior chamber
such that the compliant material transmits pressure to the
capacitor.
13. The method of claim 12, wherein capacitor comprises a first
side and a second side and wherein the complaint material is
positioned over the capacitor such that the capacitor is responsive
to pressure on each of the first side and the second side.
14. The method of claim 1, wherein the eye comprises a sclera and
wherein the proximal portion is positioned between the conjunctiva
and the sclera and wherein the proximal portion comprises an upper
surface and a lower surface and wherein the upper surface contacts
the conjunctiva and the lower surface contacts the sclera when the
distal portion is inserted into the anterior chamber.
15. The method of claim 14, wherein the upper surface comprises a
convex surface having a curvature corresponding substantially to a
curvature of the eye along the conjunctiva and the sclera and
wherein the lower surface comprises a concave surface having a
curvature corresponding substantially to the curvature of eye, such
that the proximal portion is retained between the sclera and the
conjunctiva with the conjunctiva extending over the upper surface
when the distal portion is positioned in the anterior chamber.
16. The method of claim 15, wherein the sclera comprises a Tenon's
capsule and wherein the proximal portion is positioned between the
Tenon's capsule and the conjunctiva.
17. The method of claim 15, wherein the sclera comprises a Tenon's
capsule and wherein the proximal portion is positioned beneath the
Tenon's capsule and the conjunctiva.
18. The method of claim 14, wherein the proximal portion comprises
a coil coupled to the pressure sensor such that the coil is
positioned between the conjunctiva and the sclera.
19. The method of claim 18, wherein the coil comprises a
substantially single loop antenna coupled to a second coil having a
plurality of turns.
20. The method of claim 1, wherein the eye comprises a sclera and
wherein the proximal portion is positioned between layers of the
sclera and wherein the proximal portion comprises an upper surface
and a lower surface and wherein the upper surface contacts an upper
layer of the sclera and the lower surface contacts a lower layer of
the sclera when the distal portion is inserted into the anterior
chamber.
21. The method of claim 20, wherein the upper layer is separated
from the lower layer such that the upper layer forms a flap and the
lower layer forms a bed sized to receive the proximal portion and
wherein the flap is secured over the proximal portion when the
proximal portion contacts the lower layer.
22. The method of claim 21, wherein the flap of scleral tissue
covers the sensor to decrease visibility of the sensor and fixes
the position of the sensor on the eye.
23. The method of claim 20, wherein the upper layer is separated
from the lower layer to define a pocket sized to receive the
proximal portion and wherein the proximal portion is positioned in
the pocket and the distal portion is positioned at least partially
within the anterior chamber.
24. The method of claim 23, wherein the pocket of scleral tissue
covers the sensor to decrease visibility of the sensor and fixes
the position of the sensor on the eye.
25. A method of monitoring a patient, the method comprising:
measuring an internal pressure of the eye with a pressure sensor
disposed within the eye; and determining an atmospheric pressure;
determining an IOP of the patient based on the atmospheric pressure
and the internal pressure.
26. A method of monitoring a patient, the method comprising:
determining a location of the patient; and determining an IOP of
the patient based on the location of the patient.
27. An implantable device for measuring an intraocular pressure of
an eye having an anterior chamber and a conjunctiva, the
implantable device comprising: a distal portion comprising a
pressure sensor, a proximal portion comprising a coil; and a
conformable elongate support extending between the distal portion
and the coil to couple the distal portion to the coil and wherein
the conformable elongate support is sized to position the sensor in
the anterior chamber when the proximal portion is positioned under
a conjunctiva of the eye.
28. The method of claim 27, wherein the pressure sensor comprises a
pressure transducer for placement in the anterior chamber and
responsive to pressure of the anterior chamber.
29. The method of claim 28, wherein a complaint material is
disposed over the transducer and positioned in the anterior chamber
such that the compliant material transmits pressure to the
transducer.
30. The method of claim 29, wherein the pressure sensor comprises
the transducer and the compliant material and wherein the complaint
material is positioned along a 360 degree perimeter around the
transducer such that the pressure sensor is responsive to pressure
along the 360 degree perimeter.
31. The implantable device of claim 27, wherein the pressure sensor
comprises a capacitor responsive to the intraocular pressure, the
capacitor having a first side and a second side, and wherein a
complaint material is disposed over the first side and the second
side such that the capacitive sensor is responsive to pressure on
each of the first side and the second side when positioned in the
anterior chamber.
32. The implantable device of claim 31, wherein the capacitor is
encapsulated with the complaint material.
33. The implantable device of claim 31, wherein the distal portion
comprises a maximum cross-sectional size of no more than about 0.5
mm.
34. The implantable device of claim 27, wherein the proximal
portion comprises a coil coupled to the pressure sensor such that
the coil is positioned under the conjunctiva when the distal
portion is positioned in the aqueous humor.
35. The implantable device of claim 34, wherein the coil comprises
a substantially single loop antenna coil coupled to a second coil
having plurality of turns.
36. The implantable device of claim 34, wherein the coil is
disposed on a substrate and wherein the substrate comprises a
curved shape so as to conform to a curvature of the eye.
37. The implantable device of claim 36, wherein the proximal
portion comprises a lower concave surface to contact a sclera of
the eye and an upper convex surface to contact the conjunctiva of
the eye such that the upper convex surface and the lower concave
surface correspond to the curvature of the eye when the distal
portion is inserted into the anterior chamber.
38. The implantable device of claim 37, wherein the upper convex
surface has a curvature corresponding substantially to the
curvature of the eye and wherein the lower concave surface has the
curvature corresponding substantially to the curvature of eye, such
that the proximal portion is retained between the sclera and the
conjunctiva with the conjunctiva extending over the upper surface
when the distal portion is positioned in the anterior chamber.
39. The implantable device of claim 34, wherein the coil is joined
to the pressure sensor with a conformable material extending
therebetween.
40. The implantable device of claim 34, wherein the coil is
attached to the pressure sensor with a conformable material
extending therebetween.
41. The implantable device of claim 34, wherein the proximal
portion comprises a maximum distance across of no more than about
15 mm.
42. The implantable device of claim 34, wherein the proximal
portion comprises a maximum distance across of no more than about
10 mm.
43. The implantable device of claim 34, wherein the proximal
portion comprises a maximum distance across of no more than about 6
mm.
44. The implantable device of claim 34, wherein the proximal
portion comprises a maximum thickness across of no more than about
1 mm.
45. The implantable device of claim 34, wherein the proximal
portion comprises a maximum thickness of no more than about 0.5
mm.
46. The implantable device of claim 27, wherein the distal portion
comprises a maximum thickness of no more than about 0.5 mm.
47. The implantable device of claim 27, wherein the intermediate
portion comprises a length of no more than about 10 mm.
48. The implantable device of claim 27, wherein the intermediate
portion comprises a cross sectional size within a range from about
1 to 3 French.
49. The implantable device of claim 27, wherein the intermediate
portion comprises a conformable tube extending between the proximal
portion and the distal portion and wherein the tube is disposed
over a conformable conductor and substrate extending from the
pressure sensor to the proximal portion.
50. The implantable device of claim 27, wherein pressure sensor and
the coil are disposed on a substrate such that the coil is coupled
to the sensor with substrate and wherein the conformable elongate
support comprises an intermediate portion of the substrate disposed
between the proximal portion and the distal portion and wherein the
intermediate portion of the substrate is composed of a material
having a thickness and a width such that the intermediate portion
is capable of conforming to the eye.
51. A system for monitoring an eye of a patient, the system
comprising: an implantable device to measure an IOP of the eye; an
external reader to couple to the implantable device; and a
processor system coupled to the reader to store and transmit data
measured with the implanted device.
52. The apparatus of claim 51, wherein the external reader is
configured to determine the IOP of the eye based on the measured
IOP and an atmospheric pressure, the atmospheric pressure
determined in response to a location of the patient.
53. An apparatus for measuring an intraocular pressure of an eye,
the apparatus comprising: implantable means for measuring the
intraocular pressure of the eye.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The subject application is a continuation of PCT Application
No. PCT/US2010/049461 filed Sep. 20, 2010, which is related to
61/243,847 filed on Sep. 18, 2009 and 61/335,562 filed Jan. 8,
2010, both entitled "Implantable MEMs Intraocular Pressure Sensor
Devices and Methods" the full disclosures of which are incorporated
herein by reference in their entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] People like to see. The eye is a complex organ that allows a
person to see his or her surroundings. The eye includes a cornea
and crystalline lens that form an image on the retina of the eye.
The retina of the eye senses the light image formed thereon and
transmits neural signals via the optic nerve to the occipital
cortex of the brain, such that the person can see and perceive his
or her surroundings. Unfortunately, ocular diseases can compromise
vision of the eye and may cause blindness in at least some
instances.
[0003] Glaucoma is a major cause of blindness in the United States.
In many instances, glaucoma related blindness can be prevented if
caught and managed early. Glaucoma is usually associated with an
increase in intraocular pressure (hereinafter "IOP"), that can
result in damage to the retina of the eye. Because glaucoma is
usually associated with an increase in IOP, periodic testing can be
used to monitor glaucoma in order to prevent irreversible vision
loss. For example, a person may undergo two to four exams per year
in an ophthalmologist's office, although more examination may
sometimes occur. Although treatment can be effective in many
instances, in at least some patients may continue to lose vision
under physician directed care. For example, about fifteen percent
of patients under fifty years of age may continue to lose vision
when receiving care and about thirty percent of patient over sixty
may continue to lose vision.
[0004] A significant clinical need exists to detect elevated IOP
such that appropriate medical and surgical treatment can be
delivered to control the patient's IOP and decrease vision loss.
Unfortunately, at least some of the current clinical techniques for
measuring glaucoma may not detect elevated IOP, such that a patient
can lose vision and may even become blind in at least some
instances. For example, an ophthalmic exam may only measure IOP
when the patient is in the eye clinic. In at least some instances,
the patient may undergo an increase in IOP, for example a pressure
spike, when the patient is away from the clinic. As such pressure
spikes may not be detected, the patient may not receive treatment
in time to mitigate vision loss. Further, at least some patients
may not be able to visit the eye clinic on a strict regular basis,
for example elderly patients and children, such that an increase in
IOP may not be detected in a timely manner so as to prevent vision
loss in at least some instances. Also, in at least some instances a
patient may simply forget to take his or her medicine, such that
the patient fails to follow the prescribed treatment.
[0005] Although measurements with an external IOP sensor can be
helpful, these devices that measure pressure of the eye with an
external sensor are somewhat indirect and can be inaccurate in at
least some instances, such that the measured IOP may differ from
the actual pressure inside the eye. In at least some instances,
clinically available IOP sensors determine the IOP based on the
externally measured pressure. For example, the IOP sensor can
measure pressure of the eye on the external surface of the cornea,
for example with applanation or indentation of the cornea. The
externally sensed pressure of the eye can be used to determine the
IOP of the eye based on assumptions about the anatomy and
characteristics of the patient's eye. Such assumptions can lead to
errors in the indirectly measured IOP when the anatomy of the
patient deviates from the assumed normal anatomy and
characteristics in at least some instances. For example, external
IOP measurements can be affected by scleral rigidity influenced by
topical anti-glaucoma drug therapy so as to induce errors in the
externally measured IOP in at least some instances. As a result, in
at least some instances a patient may not receive appropriate
treatment.
[0006] Although implantable shunt devices have been proposed to
treat IOP with drainage of the eye, many of these shunt devices are
not well suited for patients with IOP that can be controlled
without surgical intervention, for example medically controlled
with drugs. In at least some instances, shunts may be used a last
treatment option when other treatments such as medication and
conventional surgery have failed. The insertion of such shunt
devices can be more invasive than would be ideal, and in at least
some instances shunt devices can cause the eye of the patient to be
more susceptible to ocular trauma. For example, at least some shunt
devices are designed to drain liquid from the eye and include a
substantial chamber portion inserted into the sclera of the eye to
drain liquid, such that the sclera of the eye may be weakened in at
least some instances. Also, at least some of the current shunt
devices can include rigid components that distort tissue and may
result in ocular damage when the eye is subjected to trauma in at
least some instances. Further, implanted shunt devices can migrate
from an implanted location and can contribute to infection in at
least some instances. Therefore, integration of a pressure sensor
with a shunt device can result in an implant that is far more
invasive and an eye that is more susceptible to injury than would
be ideal in at least some instances.
[0007] It would be helpful to provide improved methods and
apparatus that overcome at least some of the above shortcomings,
for example with an implantable device capable of at least daily
direct measurement of IOP in a manner that is less invasive than
current devices, such that the improved device can be implanted in
patients with medically controllable TOP. Ideally, such methods and
apparatus can be implanted in the eye quickly and easily in an
outpatient environment, and such that many patients can receive the
benefit of direct monitoring of IOP.
BRIEF SUMMARY OF THE INVENTION
[0008] Embodiments of the present invention provide improved
systems, devices and methods for the measurement of IOP that can be
beneficial in the treatment of eyes, for example beneficial in the
treatment of glaucoma. In many embodiments, an implantable device
for measuring IOP comprises a distal portion, a proximal portion
and a conformable elongate support extending between the distal
portion and the proximal portion. The distal portion comprises a
pressure sensor, for example a capacitor, and the proximal portion
comprises wireless communication circuitry, for example a coil. The
proximal portion is configured for placement under the conjunctiva,
in many embodiments between the sclera and the conjunctiva, such
that invasiveness can be decreased substantially. For example, the
proximal portion may comprise an upper convex surface and a lower
concave surface to retain the proximal portion between the
conjunctiva and the sclera for an extended period. Also, the
proximal portion may conform to the sclera and conjunctiva of the
patient, for example with a combination of a soft housing and
flexible materials under the housing that can be bent or flexed so
as to conform the sclera and the conjunctiva. The conformable
elongate support extends between the distal portion and the coil so
as to couple the distal portion to the coil, and the conformable
elongate support is sized to position the sensor in the anterior
chamber when the proximal portion is positioned under a conjunctiva
of the eye. Positioning of the pressure sensor in the anterior
chamber has the benefit of providing a direct measurement of the
IOP of the eye. The pressure sensor may be coated with a complaint
material, such that the pressure sensor can sense pressure from a
first side of the sensor and from a second side of the sensor. Such
coating with a compliant material can allow the pressure sensor to
measure IOP accurately with pressure from many locations of the
sensor, for example along a 360 degree perimeter of the sensor and
when tissue of the anterior chamber contacts one side of the
pressure sensor. The conformable elongate support may be bent prior
to placement of the pressure sensor in anterior chamber, such that
the pressure sensor can be accurately positioned in the anterior
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A to 1C shows an eye suitable for incorporation with
an implantable sensor, in accordance with embodiments of the
present invention;
[0010] FIG. 2A shows an implantable pressure sensor comprising a
distal portion implanted in the anterior chamber to measure IOP
directly, a proximal portion comprising a coil to transmit the IOP
signal positioned under the conjunctiva and on the sclera, and a
conformable intermediate portion extending between the proximal
portion and the distal portion, in accordance with embodiments of
the present invention;
[0011] FIG. 2A1 shows an implantable pressure sensor comprising a
distal portion implanted in the anterior chamber to measure IOP
directly, a proximal portion comprising a coil to transmit the IOP
signal positioned under the conjunctiva and under a flap of sclera,
and a conformable intermediate portion extending between the
proximal portion and the distal portion, in accordance with
embodiments of the present invention;
[0012] FIG. 2A2 shows an implantable pressure sensor comprising a
distal portion implanted in the anterior chamber to measure IOP
directly, a proximal portion comprising a coil to transmit the IOP
signal positioned under the conjunctiva in a scleral pocket formed
with blunt dissection, and a conformable intermediate portion
extending between the proximal portion and the distal portion, in
accordance with embodiments of the present invention;
[0013] FIG. 2B shows surgical placement of an implantable sensor as
in FIG. 2A through an opening in the conjunctiva such that the
sensor is positioned under the conjunctiva;
[0014] FIG. 2B1 shows surgical placement of an implantable sensor
as in FIG. 2A1 on a bed of scleral tissue with a flap of scleral
tissue elevated for insertion of the sensor;
[0015] FIG. 2B2 shows surgical placement of an implantable sensor
as in FIG. 2A2 in a pocket of scleral tissue;
[0016] FIG. 2C shows a side cross-sectional view of the implantable
sensor as in FIGS. 2A and 2B, and the upper convex surface and the
lower concave surface of the proximal portion;
[0017] FIG. 2D shows top view of the implantable sensor as in FIGS.
2A to 2C;
[0018] FIG. 2E shows top view of the thin flexible substrate of the
implantable sensor as in FIGS. 2 A to 2D;
[0019] FIG. 2D1 shows top view of the implantable sensor having a
coil comprising a substantially single loop antenna coupled to a
second coil having a plurality of turns, in accordance with
embodiments as described herein;
[0020] FIG. 2F shows side view of the thin flexible substrate of
the implantable sensor as in FIGS. 2A to 2E;
[0021] FIG. 2G shows dimensions of the MEMS pressure sensor of
FIGS. 2 A to 2F;
[0022] FIG. 3 shows components of a telemetry system comprising the
implantable sensor, in accordance with embodiments;
[0023] FIG. 3A shows components of an implantable sensor as in
FIGS. 2A and 2B, in accordance with embodiments of the present
invention;
[0024] FIG. 3B shows a cross-sectional view of packaging of an
implantable sensor, in accordance with embodiments of the present
invention;
[0025] FIG. 4A shows components of an antenna reader, in accordance
with embodiments of the present invention;
[0026] FIG. 4B shows a hand held antenna reader with components
similar to the antenna reader as in 4A;
[0027] FIG. 4C shows a docking station to receive the hand held
antenna reader as in 4B;
[0028] FIG. 5 shows a method of monitoring a patient, in accordance
with embodiments;
[0029] FIG. 6A shows an implantable sensor package for direct
measurement of IOP prior to placement in an eye of a rabbit, in
accordance with embodiments of the present invention;
[0030] FIG. 6B shows the experimentally tested implantable sensor
as in FIG. 6A implanted in the anterior chamber of an eye of a
rabbit;
[0031] FIG. 6C shows a rabbit positioned near an antenna reader
with the sensor implanted as in FIGS. 6A and 6B;
[0032] FIG. 6D shows a distribution of sensor signals and a peak of
the distribution for IOP measured directly with the rabbit
positioned near the sensor as in FIG. 6C;
[0033] FIG. 6E shows pressure shifts of IOP measured directly over
time with the rabbit positioned near the sensor reader as in FIG.
6C; and
[0034] FIG. 6F shows IOP measured directly over time with
calibration for the rabbit positioned near the sensor reader as in
FIG. 6C.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Embodiments of the present invention described herein can
addresses a significant clinical need for glaucoma patients with
medically controlled IOP, particularly those patients who may be
unable to comply with a strict, regular schedule of medical
treatment such as the elderly and children. Patients having
glaucoma or other eye surgeries (e.g., cataract), eye injuries,
certain eye tumors, or eye inflammation may also benefit from
treatment with the devices and methods described herein. The
construction and shape of the device allows the device to be easily
implanted, thus reducing surgical time for this outpatient
procedure. The implant can be temporary or permanent and is
removable, and can be useful for both short term and long term
monitoring of the eye. Based on the teachings described herein, the
proximal portion can be configured to remain implanted between the
conjunctiva and the sclera for extended time, for example one year
or more. A person or ordinary skill in the art can conduct
experiments to determine empirically the parameters of the
implanted device, for example the thickness, curvature and
conformability, such that the proximal portion can remain implanted
for the extended time.
[0036] Many embodiments described herein provide a direct
measurement of intraocular pressure. The intraocular pressure can
be measured as often as practical, for example with a hand held
reader coupled to the implanted device. The measurements can be
made with sufficient frequency so as to determine the presence of
diurnal IOP curves and so as to detect IOP peaks and pressure
spikes. For example, the measurements can be generated hourly for
the first few days following surgery, and then with decreasing
frequency as the patient's pressure stabilizes. The direct IOP
measurements can be made at many locations including at home or a
doctor's office. The hand held device may automatically forward the
patient information to the treating physician, such that the
physician can monitor the patient remotely.
[0037] As used herein, the anterior segment of the eye encompasses
the anterior chamber of the eye and the posterior chamber of the
eye.
[0038] The implantable device component can be interrogated with an
antenna and reader circuitry configured to determine IOP of the eye
in response to the signal transmitted from the implanted device.
The reader circuitry is coupled to a computer processor configured
to a computer processor to store and transmit data.
[0039] In many embodiments, the implantable device comprises a MEMS
based pressure sensor for use with the treatment of glaucoma that
facilitates accurate measurement/monitoring of patient IOP in the
anterior chamber. Many embodiments utilize MEMS and wireless
technology that can provide direct, continuous and real-time data
on IOP. The implant may comprise a spiral shaped coil joined to a
pressure sensor encapsulated in a medical-grade biocompatible
material. The coil can be inserted under the conjunctiva by a
surgical implantation, such that the tip of the device with the
attached sensor comprising the pressure responsive transducer sits
inside the anterior chamber of the eye.
[0040] The implant can be removed, for example in case of adverse
events.
[0041] Following implantation, direct IOP measurements can be
obtained real-time and continuously with a data acquisition unit
that wirelessly interrogates the implanted sensor, and includes
hardware/software to control an external antenna and monitor
pressure fluctuation patterns for normal/pathological conditions.
The IOP measurement comprises a direct measurement as the
transducer of the pressure sensor is implanted in the target tissue
of interest, for example the anterior segment.
[0042] The direct IOP measurement data can be used in many
beneficial ways. For example, the direct IOP measurement data can
be used to trigger an alarm for the patient with the hand held
reader, and the data can be transmitted to a remote server and to
the office of the treating physician. The data at the remote server
can be analyzed, for example mined, to determine statistical trends
and analysis and algorithm development. The algorithm can be
embodied in instructions of a computer program of the server. The
data at the physician's office can be used by the physician to
monitor the patient.
[0043] The implantable MEMS pressure sensor device and external
telemetry may comprise components as described in U.S. Pat. Nos.
6,706,005, 6,682,490, and 6,447,449, the full disclosures of which
are incorporated by reference and suitable for combination in
accordance with some embodiments of the present invention described
herein.
[0044] FIGS. 1A to 1C show an eye suitable for incorporation with
an implantable sensor, and figures similar to FIGS. 1B and 1C can
be found in Grey's Anatomy and available on the Internet, for
example at the online encyclopedia Wikipedia
(http://www.en.wikipedia.com). The eye comprises a cornea and lens
that refract light so as to form an image on the retina of the eye.
The retina comprises a fovea comprising light sensitive cones to
detect light color sensitivity and high visual acuity. The retina
also comprise a blind spot where the optic nerve couples to the
retina. An iris is disposed over the lens and responds to light so
as to dilate in darkness and constrict in bright light, such that
the intensity of light striking the retina can be increased and
decreased, respectively. The eye comprises an anterior segment and
a posterior segment, with the lens disposed therebetween. The
anterior segment comprises an aqueous humor and the posterior
segment comprises a vitreous humor. The posterior chamber of the
eye extends between the iris and the anterior capsule of the lens
and comprises the aqueous humor. The anterior segment comprises the
posterior chamber. The liquid of the eye generally drains from the
posterior segment to the anterior segment and out Schlemm's canal
so as to maintain intraocular pressure.
[0045] Schlemm's canal, also known as canal of Schlemm or the
scleral venous sinus, comprises a circular channel in the eye that
collects aqueous humor from the anterior segment and delivers the
liquid of the aqueous humor into the bloodstream. The canal
comprises an endothelium-lined tube. On the inside of the canal,
nearest to the aqueous humor, the canal is covered by the
trabecular meshwork, and this region contributes to outflow
resistance of the aqueous humor.
[0046] With glaucoma, the drainage of aqueous liquid from the
anterior chamber is less than ideal such that IOP can increase in
the anterior chamber.
[0047] FIG. 2 A shows an implantable pressure sensor device 10
comprising a distal portion 12 implanted in the anterior chamber to
measure IOP directly, a proximal portion 14 comprising a coil to
transmit the IOP signal positioned between the conjunctiva and the
sclera, and a conformable intermediate portion 13 extending between
the proximal portion and the distal portion. The sclera of the eye
comprises Tenon's capsule disposed along a thin anterior layer of
the sclera adjacent the conjunctiva, and the implant can be
positioned between Tenon's capsule and the conjunctiva.
Alternatively, the proximal portion may be positioned under Tenon's
capsule. The implantable device may comprise a miniature,
battery-less, wireless pressure sensor that can be surgically
implanted with known surgical devices such as blades and sutures.
The implantable sensor device may comprise transducer assembly
having a capacitive pressure sensor connected to the spiral
inductor to form the resonant tank circuit of the miniature
wireless communication sensor device.
[0048] The proximal portion 14 can be sized and shaped in many ways
for placement between the conjunctiva and sclera. For example, the
housing of the proximal portion can be soft, curved and
conformable, or the underlying support can be curved and
conformable, or both the housing and underlying support can be
curved and conformable. The proximal portion 14 comprises at least
one component to transmit a signal wirelessly from under the
conjunctiva to an external device such as a reader. For example,
the proximal portion 14 can be sized and shaped for placement under
the conjunctiva and above Tenon's capsule and the sclera. The
proximal portion 14 can be conformable and shaped such that the
proximal portion 14 can remain implanted under the conjunctiva for
an extended time, for example one year or more, without undesirable
effects such as irritation and perforation of the conjunctiva. The
component to transmit a signal wirelessly may comprise many known
components to transmit a signal wirelessly, such as a coil. The
proximal portion 14 may comprise a conformable substrate such that
the substrate and coil can bend and conform to the sclera and
conjunctiva of the eye so as to minimize irritation to the eye. The
coil may be coupled to the conformable substrate in many ways, for
example with lithographic fabrication of the coil on the substrate
or printing of the coil on the conformable substrate. The
conformable substrate and coil may be coated with a biocompatible
material. The proximal portion 14 may comprise an upper convex
surface and a lower concave surface so as to decrease irritation of
the conjunctiva and sclera.
[0049] The coil can be fabricated on substrate, which together may
form a structure that corresponds to the curvature of the eye. The
structure that corresponds to the curvature of the eye may comprise
many shapes such as spherical or elliptical, and the structure may
conform to the curvature of the eye. The proximal portion
comprising the structure can be inserted in the eye in an incision
made to the conjunctiva and sutured to the sclera. The longest
dimension across the curved structure, for the example the
diameter, can be no more than about 15 mm, and a thickness T of the
plate may be no more than about 1 mm. The dimensions can be smaller
and the diameter of the proximal portion can be no more than about
10 mm, for example 6 mm, and the thickness can be no more than
about 0.5 mm, for example about 0.3 mm. Based on the teachings
described herein, a person of ordinary skill in the art can conduct
experiments to determine empirically the diameter and thickness of
the proximal portion to implant the sensor device for an extended
period of at least one year.
[0050] The distal portion 12 comprises a pressure sensor to measure
directly pressure of the anterior chamber of the eye. The pressure
sensor 12 may comprise many known pressure sensors, for example a
piezoelectric diaphragm or a capacitor, or a combination thereof.
The pressure sensor 12 may comprise a compliant material positioned
over the sensor such that sensor can measure pressure from many
locations of the sensor such as along a 360 degree perimeter and
each of a first side of the sensor and a second side of the sensor.
This sensitivity to pressure on each of the first side and the
second side can be helpful as the sensor can accurately measure IOP
when the pressure sensor contacts tissues when implanted in the
anterior chamber, for example at least one of the cornea or the
iris. Although the pressure sensor 12 may comprise many
cross-sectional sizes, in many embodiments, the pressure sensor
comprises a cross sectional size of no more than about 1 mm across
such that the pressure sensor can be inserted into the anterior
chamber, for example a cross sectional size of no more than 0.5 mm
such as 0.3 mm. The distal portion can be passed through the limbus
with a tunnel, or channel, having a dimension across, for example a
diameter across, of no more than about 1 mm, for example no more
than 0.5 mm such as 0.3 mm. The pressure sensor may comprise many
types of pressure sensors of suitable size and biocompatibility for
use in accordance with the embodiments described herein.
[0051] The conformable intermediate portion 13 can be configured to
conform to the eye in many ways. The conformable portion 18 may
comprise material that can bend or flex when the eye is subjected
to trauma, so as to decrease trauma to the eye for example when the
eye is struck with an object. For example, the conformable portion
may comprise a flexible substrate with electrical traces printed
thereon an a complaint material positioned over the traces and
substrate. Alternatively or in combination, the pressure sensor can
be located at the distal tip of a flexible tube comprising wires
that electrically connects the sensor to the coil. The tube can be
tunneled through the limbus and into the anterior chamber for
direct measurement of IOP. The tube may comprise a cross-sectional
size from about 1 to 3 French, and can be approximately 10 mm in
length. The tip or distal portion of the tube may be bent to a
prescribed curve for accurate positioning in the anterior chamber.
For example, the prescribed curve may correspond to a curvature of
the eye, such as the curvature of the eye extending between the
sclera and limbus. The intermediate portion may comprise a length
suitable for placement of the sensor at a desired distance into the
anterior chamber, for example about 1.0 to 1.5 mm, although other
distances may be used.
[0052] FIG. 2B shows surgical placement of an implantable sensor as
in FIG. 2A into an opening in the conjunctiva. An incision is made
in the conjunctiva proximal and posterior to the limbus so as to
form an opening to access the sclera. The proximal portion
comprising the curved substrate and coil is inserted through this
incision and positioned beneath the conjunctiva and on top of the
sclera and Tenon's capsule. The proximal portion 14 comprising the
curved substrate and coil can then be sutured to the sclera with
suture holes. A channel, or tunnel, can be created that extends
from the conjunctiva to the anterior chamber, and the intermediate
portion 13 tunneled into the limbus such that the distal portion 13
comprising the sensing tip extends into the anterior chamber of the
eye. The components of the implant comprising the proximal portion,
the distal portion, and the elongate support can be slid into
position together, such that the procedure can be performed quickly
and with accurate placement of the transducer in the anterior
chamber and accurate placement of the proximal portion. The distal
portion and at least a portion of the elongate support can be
passed through the incision, and the distal portion passed through
the limbus when the proximal portion is inserted into position
through the incision in the conjunctiva, such that the distal
portion is positioned in the anterior chamber when the proximal
portion is positioned on the sclera. The packaging of the proximal
portion may comprise fenestrations sized to receive sutures so as
to anchor the implantable device, and the proximal portion may be
sutured to the sclera. The conjunctiva is sutured closed.
[0053] FIG. 2A1 shows implantable pressure sensor 10 comprising a
distal portion implanted in the anterior chamber to measure IOP
directly, a proximal portion comprising a coil to transmit the IOP
signal positioned under the conjunctiva and under a flap of sclera,
and a conformable intermediate portion extending between the
proximal portion and the distal portion. The sensor is positioned
on the bed. The flap of scleral tissue is shown positioned over the
sensor.
[0054] FIG. 2B1 shows surgical placement of an implantable sensor
as in FIG. 2A1 on a bed of scleral tissue with a flap of scleral
tissue elevated for insertion of the sensor. The flap of scleral
tissue can be cut and lifted to expose a scleral bed sized to
receive the implantable sensor 10. A small incision can be formed
from the bed to the anterior chamber, which incision is sized to
receive the intermediate portion 13 and pressure sensor 12. The
implantable sensor can extend from the scleral bed to the anterior
chamber where the pressure transducer element is located for direct
measurement of IOP. The flap of scleral tissue can be positioned
over the proximal portion 14 of sensor 10, and the flap may be
sutured in place. The flap of scleral tissue can cover the sensor
to decrease visibility of the sensor, so as to provide cosmetic
benefit to the user. The flap can also fix the position of the
sensor, for example when the flap is sutured in position.
[0055] FIG. 2A2 shows an implantable pressure sensor 10 comprising
a distal portion having a pressure sensor 12 implanted in the
anterior chamber to measure IOP directly with sensor 12. A proximal
portion 14 comprises a coil to transmit the IOP signal. The
proximal portion 14 is positioned under the conjunctiva in a
scleral pocket. The pocket can be formed in many ways, for example
with blunt dissection. The conformable intermediate portion 13
extends between the proximal portion 14 positioned in the pocket
and the distal portion comprising sensor 12 positioned in the
anterior chamber.
[0056] FIG. 2B2 shows surgical placement of an implantable sensor
as in FIG. 2A2 in a pocket of scleral tissue. An opening can be
formed in the conjunctiva, and an incision is made the sclera to
the intended depth of the pocket. A blunt dissection instrument can
be passed through the opening to separate layers of sclera and form
the pocket. The pocket is sized to receive the proximal portion 14.
A small tunneling incision can be made that extends from the pocket
to the anterior chamber to receive the proximal portion 13 and the
distal portion comprising pressure sensor 12. The sensor 10 can
then be inserted into the pocket distal end first and advanced to
the final intended position with the distal portion comprising
pressure sensor 12 at least partially located in the anterior
chamber to measure IOP directly. When the sensor is positioned, the
opening can be closed, for example with sutures. The pocket of
scleral tissue can cover the sensor to decrease visibility of the
sensor, so as to provide cosmetic benefit to the user. The pocket
can also fix the position of the sensor, for example when the
opening to the pocket is sutured in position.
[0057] FIG. 2C shows a side cross-sectional view of the implantable
sensor 10 and the upper convex surface and the lower concave
surface of the proximal portion, and FIG. 2D shows top view of the
implantable sensor. The implantable sensor 10 comprises a soft
housing 14H, for example a silicone elastomer, disposed around the
coil 14C. The lower concave surface of the proximal portion 14
comprising housing 14H may comprise a spherical concave surface
having a radius of curvature R1. The upper convex surface of the
proximal portion 14 comprising housing 14H may comprise a spherical
convex surface having a radius of curvature R2. The proximal
portion 14 may comprises a substantially uniform thickness T
extending across a majority of the proximal portion. The first
radius of curvature R1 and the second radius of curvature R2 may
correspond substantially to a spherical radius of curvature of the
eye, for example a radius of curvature of the eye where the implant
is positioned such as along the interface of the sclera and the
conjunctiva. At least the housing 14H comprises the lower spherical
concave surface corresponding to the first radius of curvature R1
and the upper spherical convex surface corresponding to the second
radius of curvature R2. Although the coil 14C can be substantially
flat and disposed substantially along a plane with the housing
curved with the upper and lower curved surfaces, the coil 14C will
often comprise a spherically curved shape corresponding to the
upper and lower curved surfaces of the housing 14H, such that the
proximal portion 14 may comprise a thin profile suitable for
placement for an extended period, for example positioned above
Tenon's capsule and under the sclera for at least one year. The
curved coil may be formed in many ways, for example printed on a
curved substrate.
[0058] The proximal portion 14 may comprise a maximum distance
across, for example diameter D, that can be sized in many ways such
that the proximal portion can be positioned under the conjunctiva
for an extended period. For example, the diameter D may comprise no
more than about 15 mm across, for example no more than about 10 mm
across, such that the implant can be retained between the
conjunctiva and the sclera for an extended time. The diameter D may
comprise a smaller size, for example no more than about 6 mm
across. The substantially uniform thickness T extending across a
majority of the proximal portion 14 can be sized in many ways, and
may comprise no more than about 1 mm, for example no more than
about 0.5 mm. A person of ordinary skill in the art can determine
empirically the size of the diameter D and thickness T, based on
the teachings described herein, such that the proximal portion can
be positioned at a target tissue location for an extended period,
for example between the sclera and conjunctiva for an extended
period of at least one year.
[0059] FIG. 2G shows dimensions of pressure sensor 12S of the
distal portion 12. The pressure sensor 12S may be fabricated on the
same substrate as the coil, or can be separate and attached to the
coil. Pressure sensor 12S comprises a transducer to convert
pressure to an electrical signal, for example with capacitance. The
pressure sensor 12S comprises a length 12L, a width 12W and a
thickness 12T. The thickness 12T may comprise no more than about
0.5 mm, for example 0.4 mm or less, such that the compliant coating
can be positioned over the sensor and the resulting coated sensor
suited for placement in the anterior chamber. The length 12L and
the width 12W may comprise many sizes such that the sensor is
suited for placement in the anterior chamber, for example about 0.7
mm square with a surface area of about 0.5 mm.sup.2. The length 12L
and width 12W may correspond to many geometries such as rectangles
and squares. The sensor 12S may comprise may shapes, for example
non-rectangular shapes such as circular, hexagonal or
triangular.
[0060] FIG. 2D1 shows top view of the implantable sensor 10 having
coil 14C comprising a substantially single loop antenna MCA coupled
to a second coil 14CL having a plurality of turns. Second coil 14CL
may comprise an inductor such as a toroidal coil, for example. The
second coil 14CL may comprise a coil of the MEM circuitry formed on
the substrate as described herein.
[0061] FIG. 2E shows top view of the thin flexible substrate 14S of
the implantable sensor and FIG. 2F shows side view of the thin
flexible substrate 14S of the implantable sensor. The thin flexible
substrate may comprise a spherically curved surface that
corresponds to a radius RS of curvature of the substrate, similar
to first radius of curvature R1 and second radius of curvature R2.
The curved thin flexible substrate 14S allows the thickness of the
curved proximal portion 14 to be curved and have a thinner profile,
for example thinner than a flat substrate. The soft housing 14H and
thin flexible substrate can be combined such that the proximal
portion 14 comprising a highly conformable portion well suited for
safe placement for an extended period.
[0062] For example, a flexible substrate 14S, or support, may
comprise an outer boundary profile corresponding substantially to
the shape of the implant as seen in FIG. 2D. The flexible substrate
14S can support each of the coil 14C of the proximal portion, the
pressure sensor 12S of the distal portion, and traces of conductive
material extending between the coil and the pressure sensor, such
that the implant and flex and/or bend with the eye. The curved,
thin flexible substrate may comprise a curved flexible printed
circuitry board material with the coil printed thereon, and traces
extending to the pressure sensing transducer printed thereon. The
pressure sensor 12S comprising the transducer, for example a MEMS
capacitor chip, may comprise a component positioned on the distal
portion of thin flexible substrate 14S and affixed thereto.
[0063] The coil 14C comprising a substantially single loop antenna
14CA coupled to a second coil 14CL having a plurality of turns can
be located on the substrate 14S. The second coil 14CL comprising
the inductor can be placed on the support 14S with pads and traces
to couple to the coil.
[0064] System Components and Function
[0065] FIG. 3 shows components of a telemetry system 300 comprising
the implantable sensor. The wireless communication based pressure
sensing system may comprise several components. The implantable
sensor 10 is configured to couple to an external reader 310, for
example an antenna/reader, to determine the resonant frequency of
the pressure sensitive capacitor and inductor circuit. The
antenna/reader comprises an antenna 312 and reader circuitry 314 to
determine the resonant frequency of the implanted sensor. The
external reader 310 is configured to determine the patient IOP
based on the directly measured pressure within the eye and the
external atmospheric pressure. As atmospheric pressure can
fluctuate approximately +/-10 mm of Hg and may also change with the
elevation of the patient, the accuracy of the patient IOP reported
to the physician and patient can be improved substantially by
determining the reported IOP based on the IOP measured directly
with the implanted pressure sensor and the atmospheric pressure
external to the eye.
[0066] The external reader 310 can be configured in many ways to
determine the IOP of the patient based on the directly measured IOP
and the atmospheric pressure. For example, the external reader 310
may comprise an atmospheric pressure sensor to determine the IOP
reported to the physician and the patient based on the IOP measured
directly with implanted sensor and the local atmospheric pressure.
Alternatively or in combination, the external reader 310 may have
two way communication with an external weather site to determine
the atmospheric pressure from the external site. For example, the
external site may comprise a local weather station or web site
having a corresponding internet address, and the atmospheric
pressure where the patient is located can be determined based on
one more of postal zip code, latitude and longitude, or global
positioning system coordinates. The external reader 310 may
comprise circuitry to determine the location of the patient and use
the patient position in formation to determine the pressure where
the patient is located based on meteorological weather information.
The global positioning coordinates of the patient can be determined
in many ways, for example with location based on a cellular phone
connection of the external reader 310 or based on GPS circuitry of
the reader 310.
[0067] Atmospheric pressure associated with weather can fluctuate
slowly and on the order of +/-about 10 mm of Hg, such that
correction of measured patient IOP based on commercially available
meteorological information can be sufficient to provide accurate
determination of the patient IOP when combined with the directly
measured IOP. Also, by determining the location of the patient,
fluctuations in atmospheric pressure associated with the elevation
where the patient is located can determined and used to determine
the patient IOP. For example, the IOP reported to the physician and
patient can be determined by subtracting the barometric pressure at
the location and elevation of the patient from the directly
measured IOP to determine the corrected IOP reported to the
physician and patient. The elevation of the patient can be
determined based on the location of the patient, for example when
the patient is located at a city near sea level or a city in the
mountains. The rate of change in patient location can also be used,
for example when the patient flies and location changes
quickly.
[0068] The adjusted IOP (AIOP) for patient reporting and can be
determined in many ways based on the directly measured internal IOP
and externally measured atmospheric pressure. For example, the
adjusted IOP (.DELTA.IOP) may comprise a differential IOP
determined by subtracting the external atmospheric pressure (ATP)
from the internally measured IOP (IMIOP) with the equation
(AIOP)=(.DELTA.IOP)=(IMIOP)-(ATP).
[0069] Although a calculation is shown, the adjusted IOP can be
determined in many ways, for example with a look up table stored in
a processor.
[0070] The antenna/reader is coupled to a processor 316 comprising
a computer readable medium having instructions of a computer
program embodied to determine the intraocular pressure, for example
with a look up table, in response to the resonant frequency and the
local atmospheric pressure. The at least one processor can be
coupled to the Internet with wired or with wireless communication
circuitry and transmit the patient data to a server 320 located
remote from the patient. Alternatively or in combination, the
patient data can be transmitted to a treating physician for
evaluation of the patient. For example, the data can be transmitted
to a server located at the treating physicians office. The data can
also be transmitted to the physician with wireless cellular
communication, for example to a handheld physician communication
device such as a pager, iPhone.TM., Blackberry.TM., such that the
physician can evaluate the status of the patient and may adjust
treatment of the patient accordingly.
[0071] The external antenna/reader 310 may comprise a hand-held
ambulatory device comprising the atmospheric pressure sensor, the
processor 316 and the wireless communication circuitry such that
the patient can transmit measurement data with the wireless
communication circuitry. For example, the wireless communication
circuitry may comprise one or more of Wi-Fi circuitry or cellular
circuitry, such that the patient user can measure and transmit data
to the central server when the patient is mobile. The handheld
ambulatory external reader 310 may comprise circuitry similar to
hand held communication devices such as pagers and smart phones,
for example the iPhone.TM. or the Blackberry.TM. smart phones. The
handheld external reader 310 may comprise instructions of a
computer readable program embodied on a tangible medium to
determine the IOP reported to the physician based on the IOP
measured directly with implanted sensor and the atmospheric
pressure. For example, the atmospheric pressure can be determined
based on the location and elevation of the patient and local
barometric pressure, as described herein.
[0072] The remote server 320 may comprise data from many patients
and comprise instructions of a computer program embodied on a
programmable memory, such that the data from many patients can be
combined and analyzed. For example, the server may comprise a data
center where data are analyzed and physicians can share patient
data. Alternatively or in combination, the patient data can be
transmitted to a treating physician for evaluation of the patient.
For example, the data can be transmitted to a server 340 located at
the treating physicians office. The data can also be transmitted to
the physician with wireless cellular communication, for example
with to a handheld physician communication device 330 such as a
pager, iPhone.TM. smart phone, or Blackberry.TM. smart phone, such
that the physician can evaluate the status of the patient and may
adjust treatment of the patient accordingly.
[0073] The system 300 may comprise a processor system, and the
processor system may comprise two or more of the processor located
with the patient, the remote server, the server located at the
physician office, and the hand held physician communication device.
The remote server comprises processor comprising a computer
readable medium having instructions of a computer program embodied
thereon so as to store patient data with a database.
[0074] The hand held communication device 330 can be configured
such that the physician can transmit treatment instructions for
patient treatment so as to close the loop of the treatment for the
patient, for example with changes to medication or requesting a
patient examination. The remote server, comprises processor
comprising a computer readable medium having instructions of a
computer program embodied thereon so as to store patient data with
a database. The remote server may also forward treatment
instructions from the physician device 330 to the patient device
310.
[0075] The instructions from the handheld physician communication
device allow the physician to direct patient treatment. For
example, the physician can instruct the patient to come in for a
visit, for example to assess the status of the patient need for
additional surgical intervention. The physician may adjust the
patient medication, for example increase the patient medication.
The physician may set a target IOP for the patient based on the
clinical assessment of the patient. Some patient who have lost
vision can be more sensitive to IOP than those who have not, such
that the physician may set the target IOP for a patient with vision
loss lower than a patient who has not lost vision. For example, the
physician can set the target IOP for a patient with vision loss at
12 mm Hg, and the target IOP for a patient with no vision loss at
21 mm Hg. The physician assessment of patient vision loss can be
determined in many ways, for example with one or more of visual
fields testing or the cup to disk ratio which is known measurement
to assess the progression of glaucoma. The above treatment
instructions may comprise menu selections of hand held physician
device 330 that can be selected and forwarded to the hand held
patient reader device 310.
[0076] The handheld communication device 330 may comprise a
processor comprising a computer readable medium having instructions
of a computer program embodied thereon so as to store and display
patient data for diagnosis and treatment, for example data received
from the server. The server located at the physician office may
comprise a processor comprising a computer readable medium having
instructions of a computer program embodied thereon so as to store
patient data with the database. The remote server may comprise the
server at the physician office.
[0077] The remote server 320 can be configured to communicate with
processors of a community 350 of online users. The community 350 of
online users may comprise a plurality of processors 352. The
plurality of processors 352 may comprise, for example, a first user
processor U1 of a first user, a second user processor U2 of a
second user, a third user processor U3 of a third user and a fourth
user processor U4 of a fourth user and an Nth user processor UN of
an Nth user, for example a one millionth user. The online community
350 may comprise patients monitored with the implanted sensor
device and friends, family members and care givers of the patients.
The community of user may be connected with an online community
social networking site comprising a virtual community. For example
the online community may comprise Facebook users.
[0078] The remote server 320 can be coupled to a community of
remote online physicians 360 who can compare data and who can
provide telemedecine to members of the online community 350. The
community of remote online physicians can practice telemedecine
with a patient, for example a patient of the community of users.
The treating physician and physician device 330 may comprise a
member of the community of remote online physicians 360. Each
physician has access to a processor comprising a tangible medium
having computer readible instructoins stored thereon, for example a
smartphone, a tablet computer, a notebook computer or a desk
compuer. For example a first processor TMD1 comprising a smart
phone may be used by a first physician and a second processor TMD2
comprising a notebook computer may be used by a second
physician.
[0079] The remote server 320 can control communication and access
of the patient data, and may be configured to display information
on the displays of the online community 350 and the processors of
the community of remote online physicians. The remote server 320
can receive commands from the physician and transmit the treatment
commands to the hand held external reader 310. For example, the
physician can prescribe a target IOP for the patient based on the
physician's evaluation of the patient, and the customized physician
prescribed target IOP can be transmitted to the hand held external
reader 310. The handheld external reader may comprise instructions
of a computer program such that a message is transmitted to the
treating physician, for example an email, when the patient IOP
exceeds the customized prescribed target IOP. Alternatively or in
combination, the remoter server may comprise instructions to
transmit a message to the physician when the patient IOP exceeds
the physician prescribed IOP for the patient.
[0080] Wireless Pressure Sensor.
[0081] FIG. 3A shows components of an implantable pressure sensor
as in FIGS. 2A to 2D. The capacitive pressure sensor is connected
to the spiral inductor to create the LC resonant tank circuit of
the miniature wireless sensor.
[0082] The pressure sensors may comprise many of types of known
biocompatible pressure sensors sized for placement in the anterior
chamber.
[0083] The pressure transducer assembly 240 may comprise a
micro-electro-mechanical system (MEMS) and can be fabricated with
known methods. The coil may be fabricated on the same substrate as
the pressure sensor (1-chip). Alternatively the coil can be
fabricated on a first substrate separate and the pressure sensor
fabricated on a second substrate, and the coil coupled to the
pressure sensor (2-chip). The coil can be coupled to the pressure
sensor in many ways. For example, the pressure sensor can be joined
or attached to the coil with wires or with traces on a common
substrate such as a flex printed circuitry board, so as to comprise
a MEMS/fiex PCB hybrid device. The pressure sensor may comprise a
single chip sensor supported with a substrate, for example glass.
The pressure sensor and substrate may be positioned on a flexible
support having traces as descried above. For example, the traces
may comprise the substantially single loop antenna coupled to the
second inductor having the plurality of turns as described
above.
[0084] The pressure sensor may comprise a plurality of layers
deposited on the substrate. A layer of conductive silicon
semiconductor can be deposited on the glass substrate and shaped
with lithography and etching so as to form a lower side of the
capacitor. A layer of gold can be deposited over the silicon and
glass so as to form a lead extending from the lower side of the
capacitor to the center of the coil. A dielectric layer, for
example Si0.sub.2, can be deposited over the gold to insulate the
antenna from the lead and separate the lower side of the capacitor
from the upper side. A layer of conductive silicon semiconductor
can be deposited on the dielectric layer opposite the lower side of
the capacitor and shaped to form the upper side of the capacitor.
The upper side of the capacitor may comprise a sensing diaphragm
that bends with pressure so as to decrease spacing of the first
side of the capacitor from the second side such that the
capacitance increases when pressure increases. A layer of
conductor, for example gold, can be deposited on the second side of
the capacitor comprising the pressure sensing diaphragm, and the
conductor can be shaped to couple to the coil comprising the
telemetric antenna. A conductor, for example copper, can be
deposited at least partially over the dielectric layer and sensing
diaphragm such that the lower side of the capacitor is coupled to
the inner portion of the coil and the upper portion of the
capacitor comprising the sensing diaphragm is coupled to the outer
portion of the coil.
[0085] As noted herein, the coil may comprise the substantially
single loop coil antenna and the second coil having the plurality
of turns. The layer of conductor deposited on the substrate may be
shaped so as to comprise one or more of the single loop telemetric
antenna 14CA or the second inductive coil 14CL.
[0086] The pressure sensor may be calibrated for the elevation of
the location where the patient lives, and can have an average
pressure and frequency corresponding to the pressure at the
elevation where the patient lives.
[0087] Packaging.
[0088] FIG. 3B shows a cross-sectional view of packaging of
implantable pressure sensor 10. To protect the MEMS pressure sensor
with wireless telemetry from corrosion, the implant device may be
coated or encapsulated in a soft biocompatible polymer such as
polydimethylsiloxane (PDMS). The sensor can read pressure from all
directions as a result of its compliant enclosure 246, which is
filled with a conformable material 250 such as liquid, viscous
material, or gel (e.g., silicone, saline or other biocompatible
material). This allows pressure to be uniformly exerted on the
pressure sensor 212, such that pressure can be sensed from forces
on a side opposite the pressure sensor. For example, the implant
can be positioned such that the pressure sensor is located on a
first side of the implant opposite a second side of the implant,
and the device can measure pressure of the anterior chamber when
the second side of the implant is positioned to contact tissue of
the anterior chamber such as the cornea or iris and the first side
of the implant is positioned away from the tissue in contact with
the aqueous humor.
[0089] The transducer assembly 240 may comprise the pressure sensor
212 of distal portion 12 and a telemetric device comprising coil
214 of proximal portion 14. The transducer assembly 240 may
comprise the capacitive pressure sensor and inductor on the
substrate as described above. The assembly 240 may comprise an
elongate flexible substrate that extends so as to support both the
proximal portion and the distal portion. The pressure sensor 240
can be encased in a compliant enclosure 246 that is responsive to
external pressure. The compliant enclosure 246 may comprise a
balloon-like sac made of a biocompatible material that surrounds
the transducer assembly 240. Alternatively, the compliant enclosure
246 may comprise a gel, gelatin, or film of biocompatible
materials.
[0090] The compliant enclosure 246 can be filled with a liquid (or
a gel) 250, such as silicone, saline, or other suitable material,
that is biocompatible. The properties of the liquid 250 allow the
liquid to transmit pressure exerted against the compliant enclosure
246 uniformly against the sensing element of the pressure sensor
212, while isolating the electrical components and circuitry of the
transducer assembly 240 from corrosive media.
[0091] The illustrated pressure sensor 212 may comprise a known
configuration and can be made using known micromachining processes,
micro fabrication processes, or other suitable MEMS fabrication
techniques. Pressure sensors of this type are commercially
available from Motorola, Inc. of Schaumburg, 111. and TRW
Novasensor of Fremont, Calif. It should be understood that many
pressure sensors meet the biocompatibility and size requirements
and may be used.
[0092] The illustrated pressure sensor 212 may comprise a
piezoresistive device, and many types of pressure sensors, such as
a piezoelectric and capacitive sensors, can be substituted. The
pressure sensor 212 may comprises a substrate 260, a sensing
diaphragm 262, a plurality of patterned resistors, and a plurality
of bond pads, two of which can be associated with each of the
resistors.
[0093] The substrate 260 may have upper and lower surfaces and can
be made of silicon, but could alternatively be made of another
suitable material. The substrate 260 has a well region 269 that
extends between the upper and lower surfaces and that can be formed
using a conventional micro fabrication and bulk micromachining
processes including lithography and etching. The sensing diaphragm
262, which extends across the well region 269, can also made of
silicon and is defined by the lithography and etching processes.
The resistors and the bond pads can be formed from a metal or
polysilicon layer that is deposited, patterned, and etched in a
known manner on the lower surface 268 of the substrate 260. The
resistors could also be formed by doping the silicon using boron,
phosphorus, arsenic, or another suitable material to render a
region of the silicon with an appropriate conductivity and polarity
to create junction-isolated piezoresistors. As will be apparent to
those skilled in the art, other methods, such as SIMOX, wafer
bonding, and dissolved wafer approaches, could also be used. The
resistors can be positioned along the edges of the sensing
diaphragm 262 to detect strain in the sensing diaphragm caused by
pressure differentials. The resistors could alternatively be
positioned in another region of high or maximum strain in the
sensing diaphragm 262.
[0094] The packaging may be shaped and sized for easy insertion and
fixation. For example, the packaging may comprise a first side
having a first outer surface and a second side having a second
outer surface opposite the first side, in which the first side and
the second side extend substantially along a plane, such that the
device can be implanted between layers of the sclera. The outer
portion comprising the perimeter can be rounded, so as to decrease
point localization of forces to the scleral tissue and so as to
couple smoothly to the tissue.
[0095] Antenna/Reader.
[0096] FIG. 4A shows components of an external reader 310
comprising an antenna/reader and processor coupled to the
antenna/reader to determine the IOP. The radio-frequency probe
comprises circuitry to emit a radio frequency signal with the
antenna so as interrogate the tank circuit of the implanted sensor
device, such that the resonant frequency of the LC tank circuit can
be determined. As the resonant frequency changes with pressure, the
IOP measured with the sensor can be determined based on the
resonant frequency. The reader can house the electronics and
software, and may comprise a processor having a computer readable
medium having instructions of a computer program embodied thereon
so as to be used as a data collection, reporting and analysis
platform, for example data mining to determine the presence of
pressure spikes and trends. The processor can be programmed to
measure the IOP and predetermined intervals or predetermined times,
or both. The processor can be coupled to the Internet and the
servers as described above.
[0097] FIG. 4B shows a hand held external reader 310 comprising an
antenna reader with components similar to the antenna reader as in
4A. The hand held data reader may comprise the antenna, circuitry
to determine the resonant frequency, and circuitry similar to a
smart phone such as an iPhone.TM., such that the hand held reader
can measure, store and transmit patient data.
[0098] FIG. 4C shows a docking station 319 to receive the hand held
antenna reader as in 4B. The docking station can be configured to
charge the external reader 310 and may be used to transfer data
from the external reader to the remote server. For example, the
docking station 319 may comprise serial communication such as a
universal serial bus (USB) communication to download measurement
data from the external reader 310. The docking station 319 may
comprise communication circuitry to transmit the data from the
docking station to the remote server, for example one or more of
wireless circuitry or wired circuitry.
[0099] FIG. 5 shows a method 500 of monitoring a patient. A step
505 measures patient IOP. A step 510 determines that the patient
has glaucoma based on IOP and diagnostic tests, for example
diagnosis by a physician. A step 515 incises the conjunctiva. A
step 520 forms a conjunctival flap to expose sclera. A step 525
forms a channel extending from the conjunctiva through the limbus
to the anterior chamber. A step 530 provides the implant, for
example to the patient or to the physician. A step 535 positions
the implant with the proximal portion on the sclera and the distal
portion in the anterior chamber. A step 540 sutures the implant to
the sclera. A step 545 covers the implant with flap of conjunctiva
and sutures the conjunctiva.
[0100] A step 550 measures post-op IOP. A step 551 determines the
geographic location of patient. A step 552 determine atmospheric
pressure at patient location based on weather and elevation at
geographic location. A step 553 adjusts IOP to report based on
measured IOP and atmospheric pressure
[0101] A step 555 measures IOP regularly, for example at least
hourly or continuously, to determine the presence of pressure
spikes. A step 560 adjusts treatment based on the measured IOP. For
example, a physician can adjust dosage of a therapeutic drug or
remind the patient to take the medication as prescribed. A step 565
triggers an alarm in response to the measured IOP above
predetermined value. A step 580 transmits the data from the patient
measurement system to a server located remote from the patient.
[0102] At a step 581 a physician prescribes a customized target IOP
for the patient with the physician device based on the physician's
assessment of the patient. At a step 582, the prescribed customized
target IOP is transmitted to from the physician device to one or
more of the server or the patient device for comparison with the
measured IOP. At a step 583, the physician prescribed customized
target IOP is a compared to the measured patient IOP. At a step
584, the physician is notified when the measured patient IOP
exceeds the prescribed target IOP, for example with an email from
the server to the physician device.
[0103] At a step 585, the physician instructs patient based on the
measured IOP. For example, the physician may select instructions
from a menu. At a step 585A, the physician instructs patient to
come into office for visit. At a step 585B, the physician adjusts
patient medication. At a step 585C, the physician adjusts target
IOP. The physician can identify each of these instructions and
select one or more these steps from a menu so as to instruct the
patient.
[0104] A step 589 analyzes the data at the server, for example with
data modeling to determine statistical trends. As the communication
from the patient to the physician and back may comprise two way
communication routed through the central server, the data available
can be useful. The data analysis may comprise mining the patient
data with instructions of a computer program embedded on a tangible
medium of the remote server. A step 590 shares data among
physicians, for example with a registry of patient data for
analysis, and physicians of the online physician community can
share data with each other.
[0105] At a step 591, patients share information and data online,
for example with the online community. For example, a family member
or care giver can follow up on the care of an elderly patient who
shares data with the family member or care giver. At a step 592, a
member of the online community can ask questions of physicians, for
example the treating physician of the online physician
community.
[0106] A step 595 transmits a report on the status of the patient
to the treating physician, for example to a computer system at the
physician's office and/or to a hand held communication device such
as an iPhone.TM. or Blackberry.TM. or a pager. The report can be
transmitted based on the directly measured patient IOP. For
example, at a step 595A the report can be generated monthly when
the directly measured patient IOP remains within normal limits and
at or below the physician prescribed IOP. However, at a step 595B,
the treatment report can be generated daily, every few days, or
weekly, when the directly measured IOP equals or exceeds the
physician prescribed target or when the directly measured IOP
exceeds the range of the pre-determined upper and lower limits.
[0107] At a step 597, the physician issues a treatment command on
the hand held communication device, for example an adjustment to
the patient medication.
[0108] At a step 599, the above steps are repeated.
[0109] It should be appreciated that the specific steps illustrated
in FIG. 5 provide a particular method of monitoring a patient,
according to an embodiment of the present invention. Other
sequences of steps may also be performed according to alternative
embodiments. For example, alternative embodiments of the present
invention may perform the steps outlined above in a different
order. Moreover, the individual steps illustrated in FIG. 5 may
include multiple sub-steps that may be performed in various
sequences as appropriate to the individual step. Furthermore,
additional steps may be added or removed depending on the
particular applications. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives.
[0110] The processor system as described above can be configured to
implement many of the steps of method 500. For example, the
processor system may comprise a computer readable medium having
instructions of a computer program embodied thereon to implement
many of the steps of method 500.
[0111] Experimental
[0112] A person of ordinary skill in the art can conduct
experimental studies to determine empirically parameters of the
implantable device, such that the device can be implanted for the
extended time of at least one year, for example the diameter, the
thickness, the curvature and flexibility of each of the proximal
portion, the distal portion, and the elongate support extending
therebetween. For example, the proximal portion can be implanted
above Tenon's capsule of the sclera and below the conjunctiva for
an extended period of at least one year. Similar studies can be
conducted with additional locations of the eye, for example below
Tenon's capsule and above a majority of the thickness of sclera.
Such studies can be conducted with an animal model, for example
rabbits, and clinical studies with patients may also be
conducted.
[0113] Experimental Testing with Rabbits
[0114] The below described rabbit testing shows successful real
time direct measurement of IOP in the rabbit animal model. Similar
direct measurements of IOP can be made with the implants as
described herein, for example with the coil disposed under the
conjunctiva and the pressure sensor disposed in the anterior
chamber. The demonstrated direct measurement of intraocular
pressure of the aqueous humor and transmission of the
electromagnetic pressure signal through the corneal tissue to the
external reader correspond substantially to the direct measurement
of IOP in the anterior chamber and transmission through the
conjunctiva as described herein. For example, the transmission of
the measured EM signal through the cornea and aqueous humor
disposed between the implanted sensor and external reader comprises
a transmission distance through tissue that is at least as much as
the tissue transmission distance through the flap of the
conjunctiva for the measurement of IOP along the tissue drainage
pathway as described herein. Three (3) chip sensors as described
herein comprising 6.times.6 mm Sylgard.RTM. encapsulated biosensors
were selected for this experiment.
TABLE-US-00001 TABLE I Specifications for Implantable Sensor. Range
0-50 mm Hg (alternatively 0-60 mm Hg) Mean 18-25 mm Hg Resolution 1
mm Hg Working distance 2-4 cm (alternatively 0-6 cm) Sensor Chip
Size 6 .times. 6 mm Shape Square chip, with circular external
packaging Accuracy (absolute pressure) +/-2 mm Hg
[0115] Table I shows exemplary specifications for the implanted
device in accordance with embodiments as described herein. The
range can be from about 0-50 mm Hg for testing, although other
ranges can be used such as 0-60 mm Hg. The mean sensor reading can
be within a range from about 18-25 mm Hg. The resolution of the
sensor reading can be about 1 mm Hg. The working distance from the
measurement probe to the eye can be from about 2-4 cm, although
other ranges can be used such as 0-6 mm such that the probe can
touch the eyelid. The sensor chip size can be about 6.times.6 mm
square. The shape of the implantable sensor may comprise a square
chip with circular external packaging. The absolute accuracy of the
sensor device can be +/-2 mm Hg. New Zealand White rabbits (NZW):
Surgical procedure:
[0116] Three (3) 4-5 kg New Zealand White (NZW) rabbits (2 females,
1 male) were sedated with IM Ketamine HCL (40 mg) and Xylazine HCL
(2 mg). A retrobulbar 2% (10 mg) (0.5 ml) was administered to the
left eye of 2 animals and to the right eye of the third rabbit. The
lids were expose w speculum and topical 0.5% proparacaine HCL and
5% Betadine drops were instilled twice before surgery. A
limbal-based conjunctival flap was fashioned superiorly and a
limbal groove incision was made with a #15 Bard Parker scalpel. The
anterior chamber was entered at 12 o/c with a knife-needle and the
wound was enlarged with Castroviejo corneal scissors 3-9 o/c
superiorly. The corneal flap was reflected forward with Colibri
forceps to exposed the anterior chamber. The implantable sensor was
then inserted into the anterior chamber and positioned in-place
centrally with McPherson forceps and iris spatula. The wound was
then closed with interrupted vertical mattress 6-0 chromic sutures
and the conjunctival flap was closed with running 6-0 chromic
suture. At the end of the procedure the anterior chambers were
observed to have reformed without evidence of any wound leak.
Tobrex.RTM. (tobramycin 0.3%) was instilled in the superior and
inferior cul-de-sac. Rabbits were examined daily by gross and
slit-lamp. Topical Tobrex ointment was administered after each
examination. The implanted eyes of each animal were judged to be
clinically free of post-surgical inflammation by day 5.
In-Vivo IOP Sensing with the Implanted Chip Sensor:
[0117] The left eye of one implanted NZW (#15) was selected for in
vivo IOP sensing approximately 6 days post-implantation.
Instrumentation Overview:
[0118] An implantable chip sensor as described above was implanted
in the anterior chamber of the eye of a rabbit, approximately days
before measurements were made. The sensors are designed to shift
their resonant frequency in response to absolute pressure. The
resonant frequency of the implanted sensor is measured by an
external reader, which utilizes a custom antenna, a network
analyzer, and a custom software application running on a PC. Prior
to implantation, the pressure-frequency response of the sensor is
characterized, and is saved in a calibration file on the PC. After
implantation, the software uses the network analyzer to measure the
center frequency of the sensor, then uses the calibration file to
convert frequency to pressure.
Instrumentation Setup:
[0119] Setup Materials & Equipment:
Orthogonal antenna
Vector Network Analyzer (VNA, HP 8753C)
[0120] VNA--antenna interface hardware
Directional coupler, 1 OdB, (Olektron A2655-03)
[0121] 4 db N type attenuator
[0122] Antenna tuner & balun (custom)
Splitter (Minicircuits ZFSCJ-2-1-S)
[0123] Receiver amplifier (+34 dB, Qbit QB-164-LH) Lowpass filter
(Minicircuits BLP-100+ Coaxial cables with SMA terminations
Clamp-on ferrites (3ea, Fair-rite 0443665806)
[0124] Antenna compensation coil (custom)
[0125] Lab stand (for holding antenna)
Laptop PC (Dell D610)
[0126] Data acquisition and frequency-pressure conversion software
(Custom, AcuMEMs)
GPIB-USB adapter (National Instruments)
[0127] Tonometer (for external IOP measurement): iCare tonometer
TA01 i
Setup Procedure:
[0128] Place the antenna on a non-metallic table (the surface may
not contain a conductive loop--e.g. a metal frame around the
perimeter of the table).
"Null" the antenna
[0129] Adjust the orthogonal antenna position to minimize cross
coupling (minimize background signal on the VNA)
Adjust the tuner to achieve nominal "flatness" in the 40-50 MHz
region Compensate the effect of the patient body
[0130] Place the patient, with the un-implanted eye near the
antenna
[0131] Adjust the compensation coil position to again minimize the
background
[0132] Start the pressure-logging software on the PC, and load the
sensor file.
Procedure:
[0133] The patient was anaesthetized to minimize rapid movements
during data acquisition The implanted eye was moved close (within 5
mm) to the antenna. The software recorded data during the following
protocol
[0134] Confirm detection of the sensor in V A manual mode
[0135] Run acquisition for several minutes to establish a
baseline
Use soft-tipped swab to externally apply pressure to the sclera of
implanted eye Minimize any repositioning of the patient's head when
applying pressure Maintain applied pressure, with as much stability
as possible, for a few minutes
[0136] Gently remove the swab
[0137] Continue to record data for several more minutes
[0138] Repeat the above pressure application (discretionary)
Data:
[0139] Sensor characterization before implantation: Date of
characterization: XX/XX/XXXX Nominal center frequency (at local
atmospheric pressure):
Conditions:
[0140] encapsulated in silicone elastomer comprising Sylgard.TM.
529
[0141] placed inside of a small PVC pressure chamber
[0142] container placed directly on side of antenna cover
sensor approx. 5 mm from antenna cover
Pressure-Frequency Characterization:
[0143] Measured scale factor: -0.06612 MHz/psi x 0.019337
psi/mmHg=-0.0012786 MHz/Hg
[0144] Null frequency (0 PSI gauge): 45.12 MHz Sensor in-vivo
measurements:
Sensor characterization after implantation:
Date, Time: XX/XX/XXXX
[0145] Local pressure: 29.78 in. Hg Animal description: Rabbit,
female, approx. 4 kg, approx. 12 wks old Implantation site:
anterior chamber of left eye, sensor #XXX-Y-ZZ
[0146] FIG. 6A shows an implantable sensor for direct measurement
of IOP prior to placement in an eye of a rabbit. The implantable
sensor device comprises a chip sensor comprising a capacitive
sensor and coil embedded in a complaint transparent enclosure as
described above. The substrate supporting the coil comprises an
approximately 6 mm by 6 mm square having the circular coil and
capacitor disposed thereon. The substrate and circuitry comprise a
thickness of about 250 um and the total thickness with the complain
enclosure comprises about 500 um. The circular complaint enclosure
comprise a circular perimeter and a diameter of about 7 mm, such
that the complaint enclosure extends around and covers the corners
of the substrate with a clearance of about 0.5 mm on each
corner.
[0147] FIG. 6B shows the experimentally tested implantable sensor
as in FIG. 6A implanted in the anterior chamber of an eye of a
rabbit. The sensor is implanted under the cornea and above the
pupil and can be readily seen in the eye of the rabbit.
[0148] FIG. 6C shows a rabbit positioned near an antenna reader
with the sensor implanted as in FIGS. 6 A and 6B. The head of the
rabbit is positioned near the telemetry coil of the reader for
direct measurement of IOP.
[0149] FIG. 6D shows a distribution of sensor signals and a peak of
the distribution for IOP measured directly with the rabbit
positioned near the sensor as in FIG. 6C. The peak of the
distribution corresponds to a measured IOP of about 3 mm of Hg.
This direct measurement of IOP compared well with a known
veterinary tonometer (Icare.TM. VET) commercially available from
Icare of Finland.
[0150] FIG. 6E shows pressure shifts of IOP measured directly over
time with the rabbit positioned near the sensor reader as in FIG.
6C. The amplitude signal corresponds to the IOP of the eye and is
measured in units that correspond to mm of Hg. The direct IOP
measurement is shown for about 45 seconds. The amplitude of the
signal (arbitrary units) goes from -0.5 to 1.5, and 0 corresponds
to an IOP of 0. The signal from about 5 seconds to about 30 s has
an amplitude of about 0.2 to 0.3 and corresponds to an IOP of about
3 to 4 mm of Hg. To evaluate the real time response of the
implanted sensor, the eye was touched with a Q-tip.TM. cotton swap
at about 30 seconds (shown with first vertical arrow), and the
measured IOP elevated substantially. The Q-tip.TM. was removed and
the measured IOP went negative. The Q-tip.TM. cotton swap was
applied again at about and the pressure similarly elevated (shown
with second vertical arrow). The directly measured IOP increase was
verified with the external tonometer that showed an IOP of about 13
mm Hg. Upon removal of the cotton swab, the IOP decreased to about
3-4 mm Hg at 45 seconds.
[0151] IOP measurements using iCare tonometer:
[0152] Initial IOP of unimplanted eye: 6 mmHg
Initial IOP of implanted eye: 3 mmHg
Pressure Change Test on Implanted Eye:
[0153] 3 mmHg (initial pressure)
16 mmHg (with swab applying pressure to sclera)
[0154] 21 mmHg (2nd measurement with swab applying pressure to
sclera)
Recorded Data from "Reader":
[0155] Fc used for measurements: 45.0 MHz (center of scan
range--not necessarily 0 psi frequency)
[0156] Span used for measurement: 5.0 MHz
[0157] Changes in the center frequency of the sensor are produced
by changes in absolute pressure. To resolve relative (gauge)
pressure, local atmospheric pressure can be accounted for. The data
in the graph was manually adjusted for offsets in MS Excel. Time is
not scaled in the graph, but each point represents approximately 15
seconds between acquisitions. Changes in center frequency can also
result from other environmental effects, including presence of
nearby metal, the patient body, and motion artifacts. It can be
important to minimize motion artifacts, to avoid placing the
antenna near metal objects, and to compensate for the effects of
the patient body (using the compensation coil). The large
excursions around samples 22-30 in FIG. 6F are motion artifacts,
for example.
[0158] The signal from the sensor was readily detectable at
approximately 45 MHz. During the testing, the frequency shifted
readily (downward) with the application of pressure on the sclera
(using a swab). The corresponding pressure shifts, as measured by
the sensor and reader, were larger than similar readings taken
subsequently with the tonometer.
[0159] FIG. 6F shows IOP measured directly over time with
calibration for the rabbit positioned near the sensor reader as in
FIG. 6C. Direct measurement of IOP is shown to about 100 seconds,
and the calibrated measured IOP is shown in mm of Hg. The
measurements show increases in measured IOP when the swap if
applied to the sclera, and decreases in the directly measured IOP
when the swab is removed. Although some measurement artifacts are
shown, the data can be filtered to remove these artifacts, for
example with digital filtering. Also, lower IOP after applied
pressure is consistent with recovery of the eye and ocular
tissues.
CONCLUSIONS
[0160] The implantable, wireless sensors are capable of measuring
intra-ocular pressure changes. Further testing can characterize the
absolute and relative accuracies of the sensor and reader
measurements over the range, for example simultaneous external
indirect measurements and internal direct measurements.
[0161] Although the above experiments show good signal
measurements, one of ordinary skill in the art can make
improvements. For example, it may be helpful to strengthen the
signal from the sensor and enhance its sensitivity to pressure.
Also, the sensor and reader may be configured so as to have less
sensitive to environmental effects.
[0162] While the exemplary embodiments have been described in some
detail, by way of example and for clarity of understanding, those
of skill in the art will recognize that a variety of modifications,
adaptations, and changes may be employed. Hence, the scope of the
present invention shall be limited solely by the appended claims
and the full scope of the equivalents thereof.
* * * * *
References